We cannot stress this enough: the likelihood of dangerous weather Wednesday – including flash floods, large hail, high winds and the potential for tornadoes – is very high.
We’re going to keep this report in very blunt and very simple terms. First up is the CAPE 3000+ imagery, or Convective Available Potential Energy:
With a CAPE measure, anything over 1500 is cause for concern. The forecasted system pushing into the area tomorrow is at the peak of the charts at 3000.
Next up, realtive helicity:
To simplify, helicity measures wind shear, and the twisting and turning of winds vertically, all of which cause thunderstorms to spin and drop tornadoes. Over 150 is an eye-raiser; over 600 is considered extreme. We are at 800-plus in parts of the area tomorrow. (It is important to note that this is not a radar reading, which we are all familiar with.)
And finally, the National Weather Service’s statement from Tuesday night:
CLUSTERS OF THUNDERSTORMS WITH HEAVY RAIN AND SOME SEVERE HAIL
IN THE MORNING WILL GIVE WAY TO A MORE SIGNIFICANT SEVERE
THUNDERSTORM RISK WEDNESDAY MID AFTERNOON THROUGH THE EVENING.
ALL HAZARDS ARE POSSIBLE DURING THIS TIME PERIOD…INCLUDING VERY
LARGE HAIL…DAMAGING WINDS…LOCALIZED FLASH FLOODING…AND
TORNADOES. THIS RISK IS FOR THE ENTIRE AREA.
.SPOTTER INFORMATION STATEMENT…
SPOTTERS MAY BE NEEDED LATE TONIGHT IN NORTH CENTRAL ILLINOIS…BUT
MORE LIKELY NEEDED IN MUCH OF THE AREA ON WEDNESDAY.
The chance for very severe, dangerous weather Wednesday afternoon through Wednesday evening is extraordinary. These are similar to the types of data that were being produced prior to the April 9, 2015 tornado which ravaged Fairdale, the most powerful tornado in the U.S. last year.
Please, stay advised of local conditions. Check the batteries in your weather radio; if you don’t have one, buy one. Keep your cell phone charged. And if the weather turns for the worst, do not wait to hear the tornado sirens before you take cover.